Electrical remote control



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ELECTRICAL REMOTE CONTROL Filed Sept. 3, 1942 8 Sheets- Sheet 1 J27 V922$01: USKAR 5757745 Sept. 25, 1945. o. STETTLER 2,385,557

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ELECTRICAL REMOTE CONTROL Filed Sept. 3, 1942 8 Sheets-Sheet 5 0.STETTLER ELECTRICAL REMOTE CONTROL Sept. 25, 1945.

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0. STET TLER ELECTRICAL REMOTE CONTROL Filed Sept. 3, 1942 8Sheets-Sheet 8 US'KAH STE 7 71 EF? 5 4uZ my 1.14% forzzeys PatentedSept. 25, 1945 ELECTRICAL REMOTE CONTROL Oskar Stettlei, Zurich,Switzerland, assignor to Philips Lampcn A.-G., Zurich, Switzerland, acorporation oi Switzerland Application September 3,1942, Serial No.457,241

In Switzerland May 17, 1941 18 Claims. (Cl. 171453) This inventionrelates to remote control apparatus including a tele-controlled objectprovided with control members which are adjustable in accordance withcontrol signals received from a transmitter.

The object of the invention is to enable the controlling movement of aplurality of arbitrarily actuated control members of a transmitter to besimultaneously transmitted, sensitively and continuously (not stepwise)from a transmitter to the corresponding control members of thetele-controlled object with substantially complete synchronism oi thecontrolling and controlled members, and to do this with devices andsources of power which do not take up much room, do not weigh much, andare very unresponsive to disturbing influences According to the presentinvention the control members of the tele-controlled object are actuatedby bodies of air, the pressure of which is continuously variable underthe action of regulating members forming part of electro-pneumatic relaymeans tuned to respond to control signals comprising variations in thefrequency or/and amplitude 01' a number of alternating currents each ofwhich is allotted to one of the said control members, whereby thecontrol members can be adjusted continuously in accordance with theadjustment of continuously variable control members of the transmitter.

The invention will now be described with reierence to the accompanyingdrawings, in which:

Fig. l is a diagrammatic representation of an. apparatus according tothe invention for the remote control of an aerial vehicle.

Fig. 2 shows a joystick ior actuating three control members of thetransmitter.

Fig. 3 shows a different form of a manually actuated means for actuatingthe control mem bers of the transmitter.

Fig. 4 is a circuit diagram of a tuningfork oscillator forming part ofthe electro-pneumatic relay means.

Fig. 5 and Fig. 6 are diagrams showing the mutual relationship of theresonance curves of a frequency controlled electro-pneumatic relay andof an amplitude controlled relay, respectively.

Figs. 7 and 8 are diagrammatic representaticns of two different forms ofregulating means for varying the voltage as a function 01' the positionof the control member of the transmitter. .Fig. 9 is a circuit diagramof a transmitter apparatus for controlling four movements.

Fig. 10 is a diagrammatic view showing the actuation of a resonator bymeans of a polarized relay.

Fig. 11 is a diagram showing the curves of the control frequencies forthree symmetrical movements and one non-symmetrical control movement.

- Fig. 12 is ,a diagrammatic representation of a resonator associatedwith a slide valve and pressure nozzle forming part of theelectro-pneumatic relay means.

Fig. 13 is a diagram showing the air outflow volume from the nozzle as afunction of the amplitude of the resonator and of the time.

Fig. lid, 14b and show resonators associated with nozzles of differentshapes.

Fig. 15 is a diagrammatic view showing the manner in which theelectro-pneumatic relay means actuates a control member of thetelecontrolled object.

Fig. 16 is a diagrammatic view showing the conditions or flow oi the airwhen the slide valve is attached to the side of the resonator.

Figs. 17 to 19 show, respectively, a side elevation partly in section,an end elevation, also partly in section, and a top plan view of a constructional form of electro-pneumatic relay.

Fig. 20 is a top plan view of the relay corresponding to Fig. 19 withcertain of the parts re moved.

Figs. 21a and 21b show two views at right angles to one another on alarger scale of one term oi resonator.

Figs. 21c and 21d show two views at right angles to one another on alarger scale of am other form of resonator.

Figs. 22:: and 22?: show two elevations at right angles to one anotherOn a larger scale of a detail of the upper part of the electro-pneumaticrelay shown in Fig. 19.

Fig. 23 is a vertical section of a detail of the lower part of theelectro-pneumatic relay shown in Fig. 19, also on a larger scale, and

Figs. 24a and 24b show two elevations at right angles to one another ona larger scale of a further detail of the electro-pneumatic relay shownin Fig. 19.

Fig. 25 is a side elevation partly in vertical section of a modifiedform of electro-pneumatic rela 26 shows on a larger scale a sideelevation partly in section of a detail of the relay shown in Fig. 25.

Fig. 27 shows on a larger scale a side elevation artly in section ofanother detail of the relay shown in Fig. 25, and

Fig. 28 is an end elevation partly in section of the lower portion ofthe detail shown in Fig. 27;

Fig. 29 is a side elevation of a nozzle block for five air nozzles.

Fig. 30 is a diagram illustrating the dependence of the pressure behindthe control slide valve as a function of the amplitude of thedisplacement of the slide valve.

Figs. 31 and 32 are a side elevation and pla respectively of a workingcylinder for actuating a control member of the tale-controlled object.

Fig. 83 shows an arrangement of working cylinders for the directactuation of aircraft flight control members.

Fig. 34 is a vertical section through a servo motor for controlling asingle-acting working cylinder.

Fig. 35 is a horizontal section of a detail of the servo-motor shown inFig. 34.

Fig. 36 shows diagrammatically in section the general arrangement of aservo-motor for a double-acting working cylinder.

Fig. 37 shows a differential pressure servomotor in longitudinalsection.

Fig. 38 is a diagrammatic representation in perspective of an apparatusinstalled on board an aerial vehicle for the wireless control thereof.

Fig. 39 shows diagrammatically an electrically A. Transmitter side. -Acontrol set I. a -transmitter II, a feeding set III, a transmittingaerial IV.

B. Receiver side.A receiving aerial V, a receiver VI, batteries VII, anelectro-pneumat c resonance relay (E. P. R. relay) VIII, positioningdevices with servo-control for the fli ht control members. i. e. therudder, ailerons, elevators and so forth IX, X, XI, XI, areservoiv ofcompressed air XIII, a high-pressure reducing valve XIV, and alow-pressure reducing valve XV.

A. Transmitter side-(1) Low-frequency generator.-Every movement executedwith the joystick i or with some other control member i3, Fig. 3, actsupon a low-frequency generator Hi, Figs. 2 and 3. pertaining to thismovement. The control member i3 acts on a single low frequency generatori4, while the joy-stick is adapted to act on three generators i6, ismovable in all directions and is provided with adjustable end stops (notshown) for limiting the extent of the control movements. To eachposition of the control member i3 there corresponds a definite frequencyor a definite output voltage of the associated low-frequency generatorit, while to each position of the joystick there corresponds a definitefrequency or'definite output voltage of each of the associated lowfrequency generators.

In order that the transmission of the individual control operations maybe mutually quite inasaaecv dependent, the ranges of frequency of theindividual low-frequency generators ii are when possible so selectedthat their fundamental frequencies and the harmonics thereof do notoverlap in any of the possible relative positions of the control membersi, i 3.

Figure 11 shows upon the lower abscissa the ranges of frequencies of thelow frequency generators on the basis of the frequency control on theprinciple of the half resonance curve, and on the upper abscissa theresonance curves of the resonators in the electro-pneumatic resonancerelay, as an example. Such a low-frequency generator l4 may forexample-be constructed on the principle of a tuning fork buzzer 20,Figure 4. Upon a tuning fork 2i there acts on the one hand anelectro-magnet 22 in the anode circuit, and on the other hand anelectro-magnet 23 in the grid circuit. After the tuning fork ii isexcited, the same is kept in vibration by a supply of vibration energyfrom the thermionic valve 25. The frequency is determined by theintrinsic frequency of the tuning fork 2i.

For the present purpose, instead of the tuning fork 2i a blade springclamped at one end is employed, as shown in Fig. 9 the frequency ofwhich is varied by shifting the point of clamping- For the constructionof low-frequency generators, any other known connections and designs mayalso be employed.

(2) Action of the control in the case of frequency-reguZation.Assuming asystem with reciprocal variation of frequency away from a mid positionfor a control movement with symmetrical working cylinders, theelectro-pneumatic resonance relay hereinafter described in detail hastwo resonators per control movement, of which the natural frequenciesare f1, f1" (Figure5). The distribution of the control frequencies isrepresented by way of example in Figure 11 for three symmetrical and oneasymmetrical control movement. The natural frequencies of the pair ofresonators are so selected with respect to one another that theresonance curves thereof touch one another or overlap slightly at theiradjacent base points. The blade spring Mil in the associatedlow-frequency generator i4 passes over a range of frequencies lyingbetween the outermost positions of the control movement in question,that is, between f1 and h".

In the zero position of the control member the frequency fl is generatedand neither of the resonators respond. Every frequency of thelowfrequency generator adjusted by the joy-stick, for instance f1+Afcorresponds to a definite amplitude of the resonator between zero andArnax, for instance Ax. The resonator II reacts to all frequencies f1+Afwithin the limits f1 and f1. corresponding to a stroke of the controlmember from the zero position in the opposite direction.

(3) Action of the control in amplitude-regulation.Besides the method ofcontrol frequency regulation for the adjusting of the amplitude of theresonator in the electro-pneumatic resonance relay, a variation of theinitial or output voltage of the low-frequency generator associated withthe resonator may be effected. This regulating is carried out in such away that the initial or output voltage in the zero position of thecontrol member is a minimum, and in both the end positions is a maximum;whereas with the frequencyceiver of a symmetrical control movement aresupplied by only one tone-generator at the transmitter, with, amplituderegulation there is allocated to each resonator of the receiver alow-frequency generator tuned to the natural frequency of said resonatorin thereof, on the transmitter. The frequencies of a pair of resonatorsin this latter system are not related to one mother. In selecting thefrequencies, however, care is to be taken that harmonics andsub-harmonics are mutually avoided. The curve of the initial or outputvoltage of a symmetrical control movement as a function of thetransmitter position K is represented by the curves U1 and Us in Figure6. In-this figure the symmetrical deflection of the control member outof a zero position is indicated on the abscissa by K. U1, dotted, is thecurve of init al or output alternating voltage of the generator I as afunction of the travel of the control member, and U2 is the same curvefor the generator II.

On the ordinate the scales-for the control voltage are indicated involts and for the resonator amplitude in millimetres. Since the courseof the curves for control voltage and for resonator amplitudes, in therange utilised, are in conformity, the two curves bear the correspondingdouble references.

The amplitude-regulator may'for instance be constructed as apotentiometer with center tap and a symmetrical distribution ofresistance, as illustrated in Figure 7. Alternatively it may for exampleconsist of two variable flux transformers having separate primary andsecondary windings and cooperating with a slidable iron core, asil1ustrated in Figure 8. The frequency of the control signals as well asthe amplitude may be varied by the control members of the transmitter,for instance by mechanically coupling the amplitude regulating means tothe frequency controll'ng members.

(4)Mi:i:er with low-frequency amplifier-The mixer combines thealternating voltages of variable frequency and amplitude furnished bythe low-frequency generators of the individual control movements into as ngle alternating voltage, by electrical addition. In Figure 9 is shownan arrangement for combined frequency and amplitude control for threesymmetrical control movements with double cylinder (for instance:elevator, rudder, aileron) and one simple control movement (forinstance: gas-regulation of the engine). The apparatus consists of fourlow-frequency generators H, with appliances mounted thereon forcontrolling the initial or output voltage, a superposer for levellingthe individual control signals, consisting of the Potent ometers P1, P2,P3, P4, the filters F1, F2, F3 and F4 for suppressing higher harmonics,and the low-frequency amplifier.

In the following, the details of the assembly for the control elementsof one of these generators H is described with reference to the righthand assembly of elements in Fig. 9. The latter shows four of thesecontrol assemblies indicated by the manipulating levers l lo, Mb, I40and Md and the associated parts.

Each of the generators i4 comprises a frequency determining element 500consisting of an E- shaped magnetic core 50! the arms 502 and 503 ofwhich are provided with magnetic windings 504 and 505, respectively.windings 504 and 505 are connected in electrical feed-back arrangementwith a discharge tube 506. The frequency of the oscillations generatedby the discharge tube 506 is controlled by the resonant frequency of avibrating blade spring 508; the electrical action of the above-notedcombination of elements in gencrating 'an electrical oscillating beingsimilar to the action of the tuning fork buzzer shown in Fig.

4. The frequency of the oscillations of the generator I4 is adjustableby varying the vibratory period of the blade spring I08 and this iseflected by varying the eil'ective length of the blade spring. As shownin Fig. 9, the effective length of the blade spring 008 is varied bymeans of a pivoted control member 500 which is coupled to a mechanicallink H0 and varies the position of a fulcrumed clamping bar Bil alongthe length of the blade spring 000.

The output circuit of the generator comprises a transformer 5i! having aU-shaped core and the primary winding N3 of which is connected to theanode-cathode circuit of discharge tube 500 through a condenser ill anda resistor Ill. The secondary windings SIB of the transformer i! areconnected in series through the adjustable potentiometer P4. In thismanner, the oscillations from all of the generators are superposedthrough the potentiometers Pi, P2, P3, P4 and individually theamplitudes of the oscillations generated are adjusted. The filters Fl,F2, F3 and F4 are interposed between the secondary windings.5l8 of thetransformer and the potentiometers for suppressing higher harmonics ofthe oscillations generated.

For varying the amplitude of each of the oscillations whilesimultaneously varying the frequency thereof, each of the controlelements 509 is pro vided with a cam element 5M which varies theposition of a fulcrumed magnetic shunt 5i8 positioned over the open yokeof the ill-shaped core of transformer M2. By varying the position of themagnetic shunt, the coupling between primary winding M3 and secondarywinding BI! is varied and the amplitude of the voltage obtained from thesecondary winding 5 i6 is correspondingly varied.

The generators it having the control assemblies Ila, Nb, and Merespectively are adapted for symmetrical control movements effected bymeans of servomotors with double cylinders, and for this purpose thecams 5!? thereof have a discontinuous symmetrical face, whereby, forinstance, at the neutral position of the control lever of controlassembly a, the output voltage of the respective generator M is aminimum. Control assembly Md is adapted for a simple control movementand for this purpose the cam 5i? thereof is provided with a continuoussurface to thereby provide a continuous variation of the amplitude ofthe output voltage throughout the frequency range of the generator. Aswitch M8 is provided in the anode circuit of each of the dischargetubes 508 for disconnecting the supply voltage when desired.

The output voltage derived from the potentiometers Pi to P4 is coupledto an amplifier comprising discharge tubes 5% and 5H and an outputtransformer 522. The circuit arrangement of the amplifier conforms tousual practice and a further description thereof is believed to beunnecessary. A regulator R consisting of a potentiometer connected tothe input electrode of discharge tube 520 serves for adjusting theoutput voltage of the amplifier.

For checking the operation of each of the generators ll, there isprovided a vacuum tube or electronic voltmeter M, the input electrode ofwhich may be selectively coupled to the secondary winding of each of thetransformers Si! by a change-over switch U. In parallel with the outputterminals, to which the communicating cable to the transmitter isconnected, is provided a pair of terminals for the addition of acathode-ray oscillograph. By the aid of this it is possible, in case ofneed, to examine the mixture of frequencies.

B. Receiver side(1) Receiving apparatus.- The receiving apparatus of theremote steering means consists essentially of the following parts:

(a) Receiving aerial,

(b) Receiver, with sources of current,

(c) Electro-pneumatic resonance relay,

(d) Pneumatic driving means for the direct actuation of the rudders andother members to be controlled,

(e) Compressed-air storage vessel with reducing valve, or air-pump withcompressed-air equalising storage vessel,

(1) Servo-motors if required, for operations calling for greater controlforces.

With direct transmission of the frequency mixture from the transmitterby means of a wire connection, the items a and b are omitted.

(2) The Electra-pneumatic resonance relay.- Since a plurality of controloperations are to be transmitted simultaneously by the methods describedthrough a single path, the control current furnished by the receiver VIconsists of a mixture of a plurality of alternating control currents,varying independently of one another in frequency or in amplitude or inboth. To resolve this mixture into its components the action ofresonance is employed, that of the mechanical resonance being adopted onpractical grounds. In the relay are mounted a number of resonators, inthe form of blade springsclamped at one end, 60 in Figure or 73 inFigures l2, 14, 14a, 14b, 14c and 1'7 to 21, 20 and 21a, 21b, 21c, 21d.These resonators are so arranged in one or two rows that they arepolarised by a common system of permanent magnets or electro-magnets,and can be excited by means of magnet coils traversed by the controllingalternating current. If these springs are of different lengths or ofdifferent masses, their natural frequencies of vibration differ from oneanother, in accordance with known laws of mechanics. In order to reduceto a minimum the initial increment time during which the amplitude ofswing rises to its working value and the subsequent decrement timeduring which the amplitude falls to zero, the lengths and masses of thesprings 60 are as small as practical considerations permit. With a givenexciter output the amplitude of the resonator is approximately inverselyproportional to the frequency, so that for the purpose of obtaininggreat amplitudes, frequencies that are as low as possible should beselected. The restoring forces (the stiffness of the springs) are soselected that the resonance points lie within a range of frequency offrom 50 to 200 Hertz (cycles) for example.

Upon the springs 60, 73 there act electro-magnetic forces, which aretaken from the mixture of alternating currents mentioned. For theconversion of the output of the electrical exciter into mechanicalvibration energy there may for instance be utilised a method adapted inthe construction of polarised relays, as illustrated in Figure 10. Theblade spring 60 carries at its upper end a soft iron armature 62, theendpiece of which can swing in front of the pole shoes 64 of the permanentmagnet 55. When the coil 68 is traversed by an alternating current thepolarity of the armature 62 located between the N and S poles varieswith the frequency of the alternating current. The armature is set invibration. If the frequency of the exciter current is not in tune withthe natural frequency'of vibration of the armature 82. comparativelystrong currents are required in order to obtain a movement. If howeverthe exciter frequency synchronises with the natural frequency of thespring 80, very small power outputs are suilicient to set the spring invibration with great amplitude.

If the frequency of the exciter current is varied, while the poweroutput is kept constant, in such a way that it passes through thenatural frequen-.

cy of the resonator, there arises, between the amplitude of theresonator and the frequency of the exciter, a relationship which isrepresented in the resonance curve M of Figure 5. In the regions offrequency considerably outside the resonance position the amplitude ofvibration is very small, and gradually dies away. As thefexciterfrequency approaches the natural frequency the amplitude rises, asindicated by the curve M of Figure 5, and reaches a maximum when theexciter frequency synchronises with the natural frequency. If thefrequency changes further in the same direction, the amplitude fallsoff, as indicated by the curve M.

The steepness of the rise, and the ratio between maximum and minimumamplitude, depend upon the damping of the spring 50, amongst otherthings. Since for the present purpose on the one hand a good efliciency(high sensitiveness of the relay) is aimed at, but on the other hand,for regulating purposes, the amplitude of vibration may be utilised as afunction of the frequency, a compromise must be arrived at in choosingthe steepness of the resonance curve M. A certain residual damping isalso required, with a view to keeping the times required for thevibrations to cease sufficiently short.

When the frequency-regulating method is adopted, in order to obtainunambiguous values for the amplitude of the resonator vibration as afunction of the exciter frequency within the range of the branch of theresonance curve of Figure 5 that is utilised, an attempt is made toobtain as large a range as possible of frequency regulation between zeroand full deflection.

This aim might be attained in a simple manner by increasing the dampingof the resonator, only in that case a correspondingly higher exciteroutput would be necessary in order to obtain a given maximum amplitude.This would unpleasantly reduce the sensitiveness of response of therelay arrangement.

By the aid of the appropriate measures in design however, it is possibleto obtain a wide range of frequency-regulation without impairing thesensitiveness by additional damping.

One means of making the natural frequency of the resonator dependentupon its amplitude consists in varying the'initial mechanical stress (ordeflection) by the aid of a magnetic force; acting on one side andvarying as a function of the amplitude.

If the resonators comprise blade springs I24 having U-shaped armaturesi25 which dip into an air gap between poles I20, I22 forming part of anelectro-magnetic system as illustrated in Figures 25 and 26 forinstance, which is excited by a pole shoe and an armature is inverselyproportional to the square of their distance between the armature andthe respective pole shoes a. Upon the ordinate is marked the magneticattracting force in grammes,'-and upon the abscissa the distance betweenthe armature and the pole shoes. The point G (Fig. 30) denotes theposition of static equilibrium between the restoring force of thestationary spring and the magnetic attraction. The initial mechanicalstress produced in the spring affects the natural frequency of vibrationat small amplitudes.

By providing a variable magnetic shunt circuit comprising a soft ironplate 209, Figure 25, the magnetic initial stress of all the springs canbe simultaneously regulated within certain limits. The plate 208 isscrewed to the yoke Hi. It is mechanically initially stressed in such away that it has a tendency to press with its other end against aclamping bar H9. Part of the flux of the permanent bar magnet I I8 isthereby short-circuited. By means of a screw M the plate 209 can withincertain limits be bent away from the bearing surface of the clamping barH9. This arrangement permits a fine regulation, without play, of themagnetic shunt circuit.

For the adjustment of the air gaps, and therefore of the magneticinitial stresses of the indiridual resonators, set screws 2| i, M2 andH3 are employed, and also a screw 2, with which the pole shoe I22, inwhich there is a slot, can be shifted.

(3) Pressure-regulation by means of the electro-pneumatic resonancerelay.By the aid of the electro-pneumatic resonance relay the controlsignals received, analysed through the medium of the electro-magneticexcitation of mechanical resonators into their components, are deliveredin proper proportions, and converted into fluctuations of pressure of apneumatic power-transmission system.

By the resonators contained in the electropneumatic resonance relay,air-paths in a lowpressure pneumatic system are according to theinvention opened and closed, without mechanical frictional lossesoccurring. A resonator may consist for instance of a blade spring l3, asshown in Figures 12, 14a, 14b, 14c, 16 to 20 and 21a, 21b, 21c, 21d,which has below its free vibrating end a light soft iron armature 1!,shown more particularly in Figs. 21a, 21b, 21c and 21d. On the resonatoris mounted a small plate 76, ground plane, which stands out at rightangles to the plane of the blade spring, as shown in Figs. 21a, 21b, 21cand 21d. This small plate may alternatively be mounted, as shown inFigure 26 at lit, at the freely vibrating end of the resonator, therebyavoiding the formation of harmful eddies as shown in Fig. 16, whichillustrates the air flow past the plate 14 when the resonator isvibrating. The plate M is located opposite to the orifice Bil of an airconduit 8! (Figs. 12 and 14) in which a raised or sub-atmosphericpressure prevails. The plate 14 or I26 is somewhat larger than theorifice 80. Between the plate M or MS which constitutes a slide valvecontrolling the flow of air through the orifice, and the orifice B0 isan air gap, which is made as small as possible. When the spring '13 isnot vibrating, the plate it completely covers the orifice 80. Hence onlya little air can escape from the orifice. When the resonator isvibrating, the orifice is wholly or partially uncovered by the plate 14twice per period. the effective area of the orifice which is uncoveredby the plate increasing as the amplitude of vibration of the resonatorincreases. The arrangement, however, may be such that the orifice isfully uncovered when the resonator is stationary, the slide valve havinga central opening of sufllcient size for this purpose, and having aplate element on either side oi the said central opening, each 01' whichis adapted to cover the orifice 80 completely.

If it be assumed, for the purpose of simplifying the exposition, thatthe quantity or air 1ssu= ing at a constant difference oi pressure isproportional to the cross-sectional area oi the orifice, and also thatthe cross-section oi the orifice is rectangular and the edge of theslide valve straight, the quantity of air issuing through the orificevaries as a function of the time, as represented diagrammatically byFigure 13. The associated positions of the plate it are shown below theaxis of the abscissae. By suitably shaping the orifice 80 on the onehand and .the edge of the plate 14 on the other hand, the functionbetween the deflection oi the spring it and the escape of air,integrated over a relatively long interval of .time, can be variedbetween fairly wide limits Lack oi proportionality between thedisplacement of the control member on the transmitter and the amplitude01 vibration of the spring 13 in the electro-pneumatic resonance relaycan be corrected for example, in such a way that proportional ratios areobtained between the stroke of the control member and the escape of airfrom the orifice 80. Figures 14a, 14b and Mo show three different formsof outlet orifice. By accurate calculation or by exact experimentaldetermination of the resonance curve, for a resonator as shown forinstance in Figures 12, 14a, 14b, 14c, 17 to 20 and 21a, 21b, 21c, 21d,it is i'ound that the curve of resonance does not, as has so far beenassumed for the purpose oi simplifying the exposition, meet the abscissaat a definitely ascertainable point, but merges asymptatically into theabscissa, after passing a small percentage below the amplitude atresonance, over a relatively lengthy range adjacent to the resonanceposition.

With pure amplitude control this point is taken into account by spacingthe frequencies of a pair of resonators far enough apart.

With frequency control the resonance positions of a pair of springs orreeds it are so selected that portions of the resonance curves,intersect one another, Fig. 5 and they do this in such a way that fromthe common foot point P an approximately linear rise 02 amplitude occursin both directions. For the purpose of diminishing the air-consumptionof the electro-pneumatic resonance relay, the slide valve it may be madewider than the orifice by the amount 2 at (Figure 5). In this case theescape oi air begins at an accurately definable point, namely at thepoint P, where the amplitude out of resonance exceeds the value no, andin the further course, up to the value Amax, is approximatelyproportional to the change of frequency.

To obviate the formation of eddy currents, the little plate may bearranged overhung as a continuation of the spring, and may vibratefreely in a slot in a continuous tube.

A further problem for the electro-pneumatic resonance relay consists inthe utilisation of the variable magnitude of the escape oi air for theproduction of proportional pressure fluctuations in the workingcylinders or in the control cylinders of a servo-motor. For this purposethe working cylinders are connected with the source of compressed airthrough nozzles that can be re ulate A compressed-air reservoir 85,Figure 15, containing air at the pressure Po, is connected with a pipe88, in which an adjustable nozzle 8! is provided. This serves forregulating the apparatus. In the pipe 88 let there be assumed to be athrottle valve 88, the position of which can be read oil on a scale 89.The position of the pointer is to correspond to the amplitude of theresonator. To the pipe 88 is connected a working cylinder 90, with apiston 98. The latter is pressed towards its initial position by aspring 92. The position occupied by the piston M at any particular timecorresponds to a position of equilibrium between the spring pressure(or, it may be, the supplementary control pressure) on the one hand andon the other hand on the pressure of the body of air contained in thecylinder 90 and the pipe which acts upon the piston 9!; that is to say,to each working pressure of the said body of air there corresponds adefinite position of the piston between its two end positions.

In the above equation X indicates the distance the piston at has beendisplaced at a pressure f(P) in the cylinder 8b, which pressure is equalto the counter pressure ,f(S) exerted by the spring 92 on the oppositeside of the piston ii i.

The two end positions will first be more fully explained. Let it beassumed that the exciter frequency of the control current lies outsidethe resonance frequency of the spring i3 (Fig. 16). The electro=magneticimpulses can only excite the spring 118 very feebly. The plate it is atrest in front of the orifice 8d. The amount of air escaping is thereforea 1:: w um, which corresponds to the cross-sectional area of the gap.Let the nozzle M be so adjusted that its cross-sectional area is forinstance about three times as great as the free outlet cross-sectionalarea when the plate M is in the closed position. The velocity of flowthrough the nozzle 87 is sl, and therefore the loss of pressure in thenozzle is also small. In the space between the nozzle and the smallplate it, that is to say, at the working cylinder 9t, there prevails apressure which is only slightly below the maximum pressure. The stressin the spring 92 is so dimensioned that in this position the same isfully compressed (Figure i The other case occurs when theelectro-magnetic excitation is a maximum, and therefore the spring itvibrates with maximum amplitude. According to Figure 13 the maximumoutlet mean value is then attained. The outlet aperture on the slidevalve is so dimensioned that the mean time value of the slide-valveaperture is for example about three times as great as the aperture ofthe nozzle 87. The consequence of this is that the pressure drop of thenozzle 8? is approximately equivalent to the gauge pressure in thecompressed air reservoir 85, that is to say, the pressure at the workingcylinder to is very small.

The spring 92 will therefore press the piston 9i into its inner endposition, and will expel the air in the working cylinder to through thevibrating slide valve i6.

Between these two end positions the pressure in the working cylinder 9d,and at the some t the position of the piston ti, depend upon theinstantaneous amplitude of vibration of the resonator. Everyintermediate position (for instance an intermediate rudder deflection)can therefore be adjusted accurately and evenly, that is to say, theadjustment does not proceed step by step.

The quantity of air escaping at the orince fluctuates at twice thefrequency of the resonator. These'fluctuations result in changes ofpressure at the working cylinder 90. A comparison of the quantityescaping in one period with the volume of compressed air in the cylinderand in the inlet pipe shows that these periodical fluctuations ofpressure, and the changes occasioned thereby in the position of thepiston 9|, can only be exceedingly small. For the rest. these vibrationsare very desirable, because the troublesome difierence between staticfriction and sliding friction is thereby eliminated. The pis-- ton 8ithereforereacts to ,very fine movements of the control member I. j;

The electro-pneumatic/ resonance relay shown in'i igures l? to 20 haseight resonators. It can therefore be used for example for foursymmetrical flight control movements with double-cylinder drive, or forthree symmetrical rudder movements with double-cylinder drive and twounsetrical flight control movements with unilateral drive.

Upon a frameconsisting of light metal or of material moulded underpressure, shown in Figures 17 to 20, the resonators are arranged ingroups of four resonators each. The resonators are tuned to vibrate atthe required frequencies by limiting the length of the springs that isfree to vibrate by using clamping pieces M of different lengths. Thesprings it are accurately guided laterally.

Since in order to reduce the ohmic losses the length of the windings ofthe exciter coils H has to be as small as possible, the resonators l3and the air conduit 88 are grouped in the manner shown in Figures 1'7 to20. Th central air conduit has two orifices kit, that is to say, itserves two resonators it.

The compressed-air inlet conduit 86 conveys air to the transverseconduits or, shown in Figure 23, which cunicate with the conduits 8!,each of which has an outlet orifice at. The admission of air to theconduits ti and the orifices 89 is adjusted by means of grub screws 96,which close the ends of the conduits at.

The shape of the slide valve apertures is the deciding factor for themaximum travel of the slide valve in any particular instance.

The amplitude of vibration, from the mid osition to thecompleteuncovering of the slide- .valve aperture on both sides, is to beas small as possible. This involves a great extension in the verticaldirection and a correspondingly small extension in the transversedirection. Assuming that the slide valve is rectangular the mostadvantageous slide-valve aperture is obtained when with maximumdeflection oi the resonator the boundary edge of the slide valvescoincides with the edge of the aperture. In Figure 14a, 14b and 1ic,three slide-valves of different shapes but of the same area areshown. 01 these, a trapezium standing on end, as shown in Figure 140,yields the minimum slide-valve travel. The slide-valve aperture shouldalso exhibit as advantageous a ratio as possible between the length ofthe boundary edge and the cross-sectional area' of the aperture, since,as mentioned above, the consumption of air with the slide valve fullyclosed is proportional to the product of the length of the boundary edgeand the distance of the slide valve. The most advantageous ratio betweenarea and periphery, as is known, is given by the circle, as shown inFigure 14b. This form however is disadvanta- 7 geous with respect to themaximum amplitude of vibration. The distance between the slide valve I4and the orifice 80 is to be made as small as possible without contactoccurring. Th plane of vibration of the slide valve I4 must be exactlyparallel to the plane of the orifice.

In order to obtain a high magnetic efficiency, the resonator I3 is madein two parts. The spring 13 i made of spring steel or phosphor bronze.For the armature, core sheet or "permalloy is employed. Th two membersmay be connected with one another by riveting or soldering. The upperend of the armature is slotted or split, and the two portions are bentat right angles in opposite directions, as shown in Figures 21a, 21b,21c, 21d. The .two exciter coils I! are each secured by the aid of awedge-piece H3 (Figs. 19 and 24a, 24b) to the central branch of themanifold. According as the output connection of the receiver isymmetrical or unsymmetrical, the coils 'I'I are or are not equippedwith a central tapping. It is advisable .to shut on? the directcurrentcomponent of the anode circuit of the output discharge tube whichenergizes the coil by means of a transformer or similar directcurrentblocking arrangement. The impedance of the coils should be matched tothe impedance of the output discharge tube, or to the impedance of thetransmission line interconnecting the output discharge tube and thecoils.

On the base plate are provided, on a central support I02, two barmagnets H4 (Fig. 17), consisting of an aluminium-nickel alloy. Inner andouter pole shoes H of soft iron are securely bolted to the magnets I I4and supported in holder pieces IIB, shown'in Figs. 22a, 222).

To concentrate the magnetic flux, and to save weight, the pole shoes IISare split or slotted in such a way that the eflective ends face oneanother only over the breadth of the resonator armatures II.

In the form of construction of the electropneumatic resonance relayshown in Figures 25 and 26, each resonator consisting of a blade springI24 and an armature I25 is attached to a slide valve I26. Th resonatorsare clamped by means of clamping pieces I21 of different lengths. Figure26 shows an enlargement of the armature I25, the pole shoes I20, I22 andthe slide valve I28. The manifold I28 (see also Figure 27) is connectedby two holders I29 with the magnet system. A manifold of thisconstruction is illustrated in Figure 29. Nozzles 20E are inserted in abrass tube 200. Air enters the nozzle through a lateral aperture 203. Bythe aid of a conically ground grub screw 204 the quantity of air can beadJusted when adjusting the plant. To the pipecoupling members 205 areattached the control cylinders or the servo-valves, as the case may be.The lower end of each nozzle is shut oil by a small plate 206. The airoutlet orifice 201 is provided with a milled surface 208 (Figures 26 to28) in front of which swings the slide valve I26, as shown in Figures 25and 26.

(4) The working cylinders for driving the controlled eZements.-'I'heaction of theworking cylinders was indicated when explaining theelectropneumatic resonance relay for an unsymmetrical control movementwithout a servo-drive (Fig. 15). The movement of the piston in theworking cylinder is thus the result of the steady state of equilibriumbetween cylinder pressure and spring pressure plus control pressure.When the cylinder pressure is variable owing to the action of theelectro-pneumatic resonance relay, the spring, in order to adapt itselfto'the existing tained, which corresponds to the zero position of thecontrol. Such a state of equilibrium is very unstable. For the zeroposition of the rudder and of the control member to coincide with oneanother would only be possible with constant transmission and receptionconditions. Since however the distance between the transmitter and thereceiver is continually altering, the conditions necessary for suchcoincidence are difficult to attain, but they may be attainedapproximately, either by means of a very efficient gain control in thereceiver, or by varying the power of the transmitter in dependence uponthe distance. Both expedients may be employed concurrently.

For all the controlling operations with central zero position andsymmetrical control abutments, resonators are normally employed inelectropneumatic resonance relays.

For the rudder-drive a double-acting differential cylinder, asillustrated for example in Figures 31 and 32 may be used. Assumefrequency control. In the zero position the control frequency is at thecommon base point between the two resonance curves (Fig. 5). Theresonators 43 are at rest. The escape of air at the two orifices is aminimum, and the pressure in the two cylinders (only one of which, i.e., cylinder 39' is visible in Fig. 23) is equal and a maximum. Sincethe two piston forces act in opposite directions, there is no resultantforce component, and the rudder I is held in the zero position (Figure33) by the symmetrically acting antagonistic springs I46. Fluctuationsof field strength, and disturbances or interruptions in the wirelesstransmission, do not therefore affect this rudder position.

When the transmitting member is moved out of the zero position, thatresonator 13 is set in oscillation for which an approximation to theresonance frequency has taken place, the amplitude of vibrationcorresponding to the degree of approximation. The vibrating resonator E3increases the escape of air. A proportional fall of pressure accordinglyoccurs in the associated working cylinder I39 (Figure 33).

The pressure in the co-acting cylinder I39 Figs. 31 and 32, which hasremained unchanged at the maximum value, predominates. The rudder IMdeflects in the direction of the cylinder I39 with the variable fall ofpressure, a state of equilibrium being reached between the pressuredifference in the two co-operating cylinders on the one hand and therestoring forces on the other hand. placed out of the zero position inthe opposite direction, the two resonators I3 are interchanged in theiroperation, and likewise the two working cylinders I39 and I39, and therudder is deflected in the other direction.

For an operating pressure, used in the electropneumatic resonance relay,of about one-tenth of an atmosphere by gauge, the known designs ofpressure cylinders are not satisfactory, because If the transmittermember (I is disthe frictional losses form too large a percentage of theforces usefully employed, and because the magnitude of the friction isdependent upon various external influences, such as temperature, orviscosity, of the oilused- A control cylinder in which the pistonfriction is reduced to a minimum is shown in Figures '31 and 32.

The inner cylinder I 35 constituting the working position is guidedco-axially in two outer cylinders I38 and I38, by guiding rods I81,connected with one another by means of cross bars I36, and bearings I38,Compression springs I40 hold the movable cylinder in its mid position.In

the space between the outer and inner cylinders is placed an indiarubberbag Ill. When the pistons I85 move in the cylinders I39 and I39, theindiarubber sheaths I, which are filled with air, roll, as it were,along the peripheral surfaces of the two cylinders, and air is expelledthrough pipes I42.

For the positive actuation of a plurality of members the doublecylinders described above maybe employed as shown in Fig. 38. Thecontrol surfaces 8 are connected by tensile members are with the crossbars I86 as shown in Figure 38. For tail-control (elevating and lateralrudders) of model aeroplanes, the control cylinders I39 and I38 may belodged in the shell or covering of the tail ltd, as shown in Figure 33.In order that there may be as few projecting parts as possible, thecylinders are in staggered relationship to the axis of rotation.

By the aid of a receiving set, which is fed directly from theelectro-pneumatic resonance relay, an effective operating pressure ofabout 0.2 kilogramme can easily be obtained.

If it is a question of controlling movable objects calling for a largeexpenditure of force, a pneumatic, hydraulic or electrical servo-deviceis employed.

In the case of a pneumatic servo-drive, a single-acting or double-actingsystem may be constructed. with the single-acting type of structure, thepiston pressure on the one hand, and the pressure of a powerfulantagonistic spring plus the back pressure of the rudderon the otherhand, counter-balance one another. Figures 34 to 36 show acompressed-air servodrive. A double-armed lever IE is mounted upon ahollow shaft IEI, which is ground into and readily rotatable in a bushI52. The bush IE2 is rotatably supported in a valve casing I53. Therotating of the bush IE2 is effected by way of rod-and-lever mechanismI56, in positive connection with the movement of the working piston I55.The transmission of power to the rudder ltd is eifected by way of aconnecting rod IES'I.

Compressed air at a gauge pressure of about atmospheres passes throughan inlet pipe IE8 into a circumferential groove I 59 in the hollow shaft.itl, and into axial grooves or ports Ito in the periphery of saidshaft. The bush I52 is provided with slots IbI which are adapted toregister with the ports Itll or with radial slots I82 in the shaft IEI,which are in open com munication with the axial bore let of the shaftand through the latter with the atmosphere.

Assuming that the control cylinder occasions a right-handed rotation ofthe hollow shaft IEI, from the position shown in Fig. 34 until the portsIBM. The piston I55 moves outwards to the right under the action of thecompressed air. The bush I5I rotates, in consequence of the motionimparted thereto by the piston I65 through the rod I54, in the samedirection as the hollow shaft IllI, until the slots IBI are covered byportions of the periphery of theshaft IBI located between the groovesI80 and the slots I02, whereby the fiow of compressed air through theslots ISI is interrupted and the piston comes to rest. If the hollowshaft Iii rotates to the left, the slots I82 are brought into registerwith the slots IEI of the bush I52, so that the compressed air containedin the cylinder I can pass into the axial bore I88, and from there intothe atmosphere. It is evident that the working piston continues to moveuntil the position of the bush IE2 relatively to the hollow shaft Iii isthe same as that shown in Figure 3a in which the slots I6I are covered.

The regulating member for a double-acting servo-cylinder is illustratedin Figure 36. The construction is substantially the same as for asingle-acting cylinder, but the compressed-air paths are modified, thatis to say, the distribution of the fresh-air grooves and exhaust slotsin the hollow shaft IBI is difierent from that of Figure 3%. Thepressure manifold in the casing I66 register with the slots ISI in therotatable bush I52, compressed air from the pipe I58 flows through theports Itli and slots IEI into the turned recess of the casi'ng I53, andfrom there into the working cylinder Ittc through a pipe H5 is here intwo parts, one part communicating with the upper pressure chamber of thecylinder and the other part with the lower one.

Figure 37 shows a type of servo-motor difier ing from the type alreadydescribed.

The pipe I is connected to the electro-pneumatic resonance relay, thepipe led with the working cylinder, and the pipe I811 to the airpump. Anindia rubber diaphragm I88 separates the pressure space of theelectro-pneumatlc resonance relay from that of the working cylinder.When the pressures are in equilibrium the diaphragm occupies its midposition. A rotary or cylindrical valve I89 is connected by a steel wireI89, in which a helical spring ItI is inserted, with the diaphragm. Arow of holes I92, in the initial position, faces a web or bridge-pieceI93 between turned grooves I84 and I95, of which the former communicateswith the atmosphere and the latter with the pump. When a difierence ofpressure occurs between the two spaces separated by the diaphragm I88,the cylindrical slide valve I88, according to the sign of thedifference, moves into the region of one of the two grooves I96, I95until equilibrium of pressure is re-established.

The purpose of this form of the apparatus is to enable the pressure inthe two working cylinders to be equalised with as little delay aspossible, since the cross-sectional areas provided in the servo-valvecan be made considerably larger than those of the electro-pneumaticresonance relay.

By the aid of the spring IQI introduced into the mechanical connectionI99, a change in the magnitude of the pressure can also be obtained. Thediaphragm let on the one hand and the circular slide valve I69 on theother hand act as a difierential piston. With an increase of thepressure prevailing in the working cylinder the spring IQI lengthens, sothat a greater deformatlon of the diaphragm I88 is necessary, in orderto obtain the same position of the slide valve,

providing a correspondingly large counter-pressure diaphragm.

Instead of a pneumatic or hydraulic servocontrol, an electrical orelectro-mechanical servo-device may of course be used. For theappropriate arrangement and. wiring there are numerous known examples.One type of construction will be here described in detail.

Referring to Fig. 39, the reversible electric motor 2H5 has anarrangement of the connections with a mid-point feed, the drive beingapplied to a control shaft 2l6 through a worm 2|! and worm-wheel segment2H3. An insulated blade spring 2l9 secured to the segment H8 has at itsfree end a contact piece which is arranged between co-acting contacts HIand 222, secured in the insulating piece 220. This insulating piece 20is connected with a double-acting piston 223,

which is a constituent part matic regulating system.

When the piston moves in one direction out of the position of rest, oneof the contacts Ht, 222 will touch the central contact, and will remainin contact with it until the motor has shifted the segment so far in thesame direction that the position of the segment corresponds to the newposition of the piston.

Automatic regulation of the conivoZ-signaZ.- When adopting the method ofregulating the resonator amplitude on the principle of the halfresonator curve, it is desirable to keep the strength of the lowfrequency control signal that flows through the exciter coil of therelay at a constant level. For the method of controlling the resonatorsby variable amplitudes of constant control frequency, however, an exactregulation of the signal strength level is an indispensableprerequisite. In wireless transmission of the con trol signal by the useof a high-frequency carrier wave between two movable objects, or betweena stationary and a moving object, it lies in the nature of the case thatin consequence of the inevitable changes of distance, great fluctuationsof field strength occur at the receiving aerial. Furthermore it is knownthat the useful field strength at the receiving aerial is also afunction of the relative positions in space of the transmitting andreceiving aerials. Both causes involve the necessity of adopting anautomatic regulation of the signal strength level having a great usefulrange. One condition essential for the attainment of the desired rangeof regulation is a sufficient transmitter power output, and anof anelectro-pneuother is a sufficient maximum sensitiveness oi the receiver.The critical limiting values are bound up with the condition that evenin the case of disadvantageous transmission conditions the controlvoltage required for the method of working of the electro-pneumaticresonance relay is available at the receiver output.

The following methods of automatic regulation of the signal strengthlevel are sug ested, the specific features of which prove more or lessadvantageous according to the particular purpose for which the distantcontrol is employed.

(1) For those purposes in which it isa question of discharging, from anaeroplane for example, a projectile equipped with a tele-steeringdevice, and in which the problem is to steer this projectile to adefinite target by the aid of the telesteering apparatus, a definiterelationship has to be established in every case between the time ofdischarge and the distance between the transmitter and the receiver.Moreover in the given examples the spreading or difiusion conditions ofelectro-magnetic waves are very close to the physical ideal case withouttaking disturbing damping effects into consideration. These areadvantageous presumptlons for the adoption of automatic control of thesignal strength level operated from the transmitter, employingmechanical means. The designs adopted for embodying this principle mayfor example be provided in the following manner:

' By actuating the starting appliance for the pro- J'ectile to besteered, a clockwork mechanism or a small electric motor is set inoperation by a mechanical or electrical coupling, and by this means iii)an eccentric sheave or disc is set in slow rotation, one revolutionhaving the duration of the longest trajectories to be considered. Aroller pressed against the eccentric sheave by a. spring varies itsdistance from the axis of the eccentric sheave or disc in the course ofthe trajectory as a function with which the transmitting energy in thecourse of the discharge is to be increased in order to obtain a more orless constant high-frequency voltage at the receiving aerial of theprojectile. The movement of the running roller is coupled, by the aid ofa rod-and-lever transmission mechanism, to the continuously actingpower-output regulator of the transmitter. After the expiration of adischarge the appliance can be restored, either by hand or automaticallyto the position of readiness.

(2) For all applications of the control described in which the distanceand the. relative position in space of the receiving aerial in relationto the transmitting aerial are variable arbitrarily and irregularlywithin wide limits, the signal strength level regulation is preferablyeifecmd on the receiver side. In principle any one of the numerousarrangements for counteracting fading, such as are employed inbroadcasting receivers, may be adopted. Since the mixture of frequenciesto be transmitted differs in its structure from that of normalelectro-acoustical transmissions, methods of regulation of the signalstrength level may be adopted which are considerably more effective thanthose of the ordinary fading-compensation means, in which, as is known,the regulation voltage is obtained from one or more diode sections ofthe demodulator stage.

With the exclusive employment of frequency regulation by the method ofthe half resonance curve, the effective value of the mixture ofalternating control voltages is independent of the adjustment of theindividual control frequencies. It is therefore possible to utilise theeffective value of this voltage in the anode circuit of the outputamplifying valve as a regulating component for the automatic regulationof the signal strength level instead of a. voltage derived from thedemodulating stage. In this way the regulating impulse for afluctuation, occurring at the input, is considerably stronger than withthe normal method, because the whole of the amplification of thereceiver is inserted in between. Preferably the method of delayregulation is adopted, in order to obtain an advantageous shape of thecurve of regulation.

This arrangement may be carried out according to the principle ofconnection illustrated in Figure 40. 30! and 302 are valves which are tobe regulated by varying the grid bias. 303 is the output valve, theanode circuit of which includes the ex-citer winding 30% of theelectro-pneumatic resonance relay. The alternating anode voltage istaken directly from this winding and supplied in a known manner, by wayof a condenser 80!, to a rectifier or diode 308. The direct voltageacross the resistance 80'! generated by rectifying the alternatingvoltage serves as a regulating voltage. It is supplied as a negativegrid bias to the grids of the valves 8M and 802 to be regulated througha filter circuit consisting of a resistance 38 and a condenser 309. Therectifier section 306 may be connected to a tapping on the anode battery8! to thereby provide a voltage delay in the action of the biasregulating voltage.

In controlling the resonators by amplitude variation of the controlfrequencies, and for mixed frequency and amplitude control, thepotential of the control voltage at the relay is a function of theposition of the regulating members, that is to say, the control voltageis variable with constant transmission conditions. In order neverthelessto be able to utilise the advantages of the maximum amplifiedcontrolling voltage, a special alternating voltage of constant frequencyand amplitude, serving onhr for the regulation of the signal strengthlevel, is preferably superposed upon the control signal at thetransmitter end. At the receiver end, in series or in parallel with therelay winding, an oscillating circuit all is coupled to the anodecircuit of the end valve 803, as shown I in Figure 41, and is tuned tothe regulating frequency. The alternating voltage of this circuit issupplied, just as described above, to a rectifier we, and the directvoltage thus obtained, with or without a delay voltage, is applied tothe grids time and 82a of the valves to be regulated. The remainingcircuit components constituting the receiver VI and the position andfunctioning of the valves 8!, 382 and see are well understood by thoseskilled in the art and a further description thereof is believed to beunnecessary.

A further method of regulating the signal strength level, shown in Fig.42, likewise uses an auxiliary signal sewing exclusively for regulatingpurposes. Instead of an electrical oscillating circult, electropneumatic control means are employed, including an additional mechanicalresonator 3i? mounted in the electro-pneumatic resonance relay, the saidresonator being set in vibration by the auxiliary signal from thetransmitter comprising an alternating current of constant frequency andamplitude, superposed on the signals for adjusting the control membersof the tele-controlled object. The amplitude is therefore still only afunction of the transmitting conditions. The variation of the inputstrength of the auxiliary signal at the receiver acts on thesupplementary resonator 3!? which controls the air flow through anorifice are in a conduit connected to a pneumatic cylinder 363, so as toproduce pressure variations in the latter in a similar manner to thepressure variations produced by the other resonators in the bodies ofair which afiect the adjustment of the control members of thetale-controlled object. The cylinder M3 has a piston or like memberwhich is in a position of equilibrium between the force of anantagonistic spring (not shown) and the pressure in the cylinder. Thispiston member, which in the arrangement shown in Figure 42 comprises adiaphragm did, is connected with the movable yoke of an iron coretransformer 3B9 interposed between the receiver and the exciter coil 3Hof the resonator 2392 in such a way that one or more air gaps Bit of thetransformer yoke become larger or smaller when the member 3M isdisplaced by pressure variations in the cylinder tit, whereby themagnetic circuit of the transformer M9, through which the mixture ofalternating currents is supplied to the electro-pneumatic resonancerelay, varies as a function of the pressure in the cylinder 5l8. Sincethe pressure in the cylinder 3H3 depends on the input strength of theauxiliary signal at the receiver acting on the exciter coil 3H throughthe transformer M9, the strength of the mixture of alternating controlvoltages supplied to the electro-pneumatic resonance relay through thetransformer is held at an approximately constant level.

Alternatively, the piston member may be connected with the slidingcontact of a potentiometer which is so connected that by varying thegrid bias of the valves to be regulated a fall 01 the input signalstrength leads to an increase in the amplification.

What I wish to claim and secure by U. S. Letters Patent is:

1. Apparatus for remotely controlling the position of an element insynchronism with the movement of a control member, comprising a. sourceof alternating voltage, means to vary said voltage smoothly andproportionally to the change in the position of said control member,means to transmit the so varied voltage, an electrically operablevibratory member responsive to the said varied voltage the amplitude ofthe vabration of said member being variable in accordance with thevariations of the voltage, a gas column having an inlet port and anoutlet port, a source of gas under pressure connected to said inletport, a valve movable relatively to said outlet port the valve beingactuatable by said vibratory member and being adapted to vary thepressure of said gas column in a smooth and continuous manner and proportional to the amplitude of movement of said vibratory member, and meansactuated by variations in the pressure of said gas column forcontrolling the position of said element.

2. Apparatus as claimed in claim 1, including as voltage varying meansmeans for varying the frequency and the amplitude of the alternatingvoltage smoothly and proportionally to the movement of the controlmember.

3. Apparatus as claimed in claim 1 comprising in the means for varyingthe voltage a variable i'lux transformer coupled to the source ofalternating voltage, and means connected with the control member forvarying the flux of said trans== former.

4. Apparatus as claimed in claim 1 wherein the valve actuable by thevibratory member is a plateshaped element secured to the vibratorymember and positioned over the outlet port to obstruct and free the sameduring the vibrations of said member.

5. Apparatus as claimed in claim 1 wherein the valve actuable by thevibratory member is movable in a. plane parallel to and closely adjacentthe plane of the outlet port in proportion to the displacement of thevibratory member.

6. Apparatus as claimed in claim 1 wherein the inlet port has anadjustable passage aperture, and comprising means to adjust saidaperture to produce a substantially small pressure drop through theinlet port when the outlet port is obstructed by the valve and toproduce a substantially large pressure drop through the inlet port Iwhen the outlet port is freed by the valve.

7. Apparatus as claimed in claim 1 comprising as means actuated by thevariable pressure in the gas column a working cylinder connected to theas column between the inlet and outlet ports, and means operable inaccordance with pressure in the working cylinder for controlling theposition or the element to he controlled.

8. Apparatus as claimed in claim 1 including in combination with thevibratory member responsive to the varied voltage a U-shaped armaturesecured to the vibratory member, a magnet having pole shoes which forman air gap with respect to which the armature is movable, and means ioraltering the strength of said magnet in accordance with the variedvoltages.

Apparatus as claimed in claim 1 comprising a cylinder connected to thegas column, and as means actuated by the variable pressure in the gascolumn a piston within said cylinder and spaced therefrom, and aflexible gas-impervious envelope lcetween the piston and cylinderconnected at one end to the cylinder and at the other end to the piston,to form a pressure responsive chamber oi variable volume between thecylinder and the piston and adapted to support the piston duringrelative movement of the cylinder and piston.

lllelpparstus as claimed in claim 1 wherein the means to transmit thevaried voltage comprises a source of a high frequency carrier wave and amodulator for impressing the varied voltare on the carrier wave,including means for varying the intensity of the modulated carrier wave.

ll. Apparatus as claimed in claim l wherein the means to transmit thevaried voltage comprises a source of a high-=irecuency carrier wave, amodulator for impressing the varied voltage on the carrier wave, andmeans for interceptinathe modulated carrier wave, the intercepting meanscomprising an amplifier, a demodulator for the carrier wave and meansfor varying the degree of amplification of the carrier wave proportionalto the intensity of the demodulated voltage for producing demodulatedvoltage of substantially constant amplitude.

l2. Apparatus for remotely controlling the position oi an element insynchronism with the move ment cl 9, control member, comprising twosources oi alternating voltage, means for varying one of said voltagesroportionately to the change in the position of said control member, asource of high frequency carrier wave, means for modulating said carrierwave in accordance with the varied voltage and the unvaried generatedalternating voltages, means to transmit the so modulated carrier wavewith the varied and unvaried voltages superimposed to each other and tosaid carrier wave, means to intercept the modulated carrier wave, onamplifier and a demodulator for the in terceptecl carrier wave derivingto obtain therefrom the unmodulated varied voltage and the non-variedtransmitted alternating voltage, two electro=mechanical resonators eachcomprising a vibrating member responsive to one of the trans mittedvoltages, two gas columns having inlet and outlet ports, a source of gasconnected to the inlet ports, two valve members each actuated by one ofsaid vibratory members covering said outlet ports and adapted to va ythe pressure of the gas columns in a smooth and continuous manner andproportional to the amplitude of movement of the vibratory members,means actuated by variations in the pressure of the gas columncontrolled by the varied voltage for controlling the position of saidelement, and means actuated by variations in the pressure of the gascolumn controlled by the non-varied transmitted voltages for varying thedegree of'ampliflcation of the intercepted modulated carrier wave.

13. Apparatus as claimed in claim 12 wherein the means for varying thedegree of amplification of the intercepted wave comprises a pressurecylinder actuated by the variations in pressure in the gas columncontrolled by the other of the transmitted voltages, a source of biasingvoltage for said amplifier and a potentiometer actuated by said pressurecylinder for varying the amplitude of the biasing voltage.

14. Apparatus for controlling the movement of an element about a givenposition from a remote location in synchronism with the movement of acontrol member about a corresponding given position at said remotelocation, comprising two sources oi alternating voltages of differentfrequencies and oi given intensity at the remote location, means forselectively varying the intensity of said voltages smoothly andproportionately to the change in the position of the control member fromthe given position, means for transmitting the so varied voltagessimultaneously over a common path and converting the transmittedvoltages into two different groups of mechanical vibrations, each grouphaving a resonant frequency different from the other and equal to thefrequency of one of said voltages and each having an amplitude ofdisplacement within the resonant range proportional to the amplitude ofthe excit= ing voltage, means for electropneumatically controlling thepressure of two columns of gas in a smooth and continuous manner each bymeans oi one of said groups of vibrations and in proportion to theamplitude of movement of the same, and means for controlling theposition of said element in a smooth and continuous manner by variationsin the pressure of the gas columns.

l5. Apparatus for remotely controlling the po-- sition of an element ata receiver movable relatively to a transmitter and in synchronism withthe movement of a control member at the transmitter, comprising a sourceof alternating voltage at the transmitter, means for varying saidvoltage smoothly and proportionally to the change in the position of thecontrol member at the 'ransmitter, means for modulating the so variedvoltage on a high frequency carrier wave, means for transmitting themodulated carrier wave and varying the intensity of the modulatedcarrier wave proportional to the distance between the transmitter andthe receiver so as to maintain a constant field intensity at thereceiver, means for intercepting and demodulating the transmittedcarrier wave, means for electro-pneumatlcally controlling the pressureof a column of gas in a smooth and continuous manner pro portional tothe variations of the demodulated voltage, and means for controlling theposition of said element in a smooth and continuous mannor by variationsin the pressure of the gas columns.

16. Apparatus for remotely controlling the movement of an element abouta given position in synchronism with the movement of a control memberabout a corresponding given position, comprising a source of alternatingvoltage of given frequency, means for varying the frequency of saidvoltage about the given frequency smoothly and proportionally to themovement of the control member from the given position, means formodulating the so varied voltage on a high frequency carrier wave, meansfor transmitting, intercepting and amplifying the modulated carriercally represented by a curve, the curves for all sets having a commonfoot point, means for electro-pneumatically controlling the pressure ofindividual columns of gas in a smooth and continuous manner inaccordance with the mechanical vibrations and in proportion to theamplitude of movement of the same, and means for controlling theposition of said element in a smooth and continuous manner by variationsin the pressure of the gas columns.

17. Apparatus for remotely controlling the movement of an element abouta given position in synchronism with the movement of a control memberabout a corresponding given position, comprising two sources ofalternating voltages of dliferent frequencies and of given intensity,means for selectively varying the intensity of one of said voltagessmoothly and proportionally to the change in the position of the controlmemher from the given position, a third source of alternating voltage ofanother frequency and of constant amplitude, means for modulating thethree voltages on a high frequency carrier wave with the three voltagessuperimposed thereon, means for transmitting the modulated carrier wave.means for intercepting and amplifying the modulated carrier wave, meansfor demodulatlng the said carrier wave, means for separating the saidthird voltage from the other demodulated voltages, means for varying thedegree of amplification of the intercepted modulated wave inverselyproportional to the amplitude of said separated voltage, means forconverting the other demodulated voltages into two groups of me chanicalvibrations, each group having a resonant frequency diflerent in valueand equal to the frequency of one of said voltages and each having anamplitude of displacement within the resonant range proportional to theamplitude of the exciting voltage, means for electro-pneumaticallycontrolling the pressure of two columns of gas in a smooth andcontinuous manner, each in accordance with a group of said vibrationsand in proportion to the amplitude of movement of the same, and meansfor controlling the position of said element in a smooth and continuousmanner by variations in the pressure of the gas columns.

18. Apparatus as claimed in claim 17, including means for varying thepressure of a third body of gas by means of said separated voltage andvarying the degree of amplification of the intercepted modulated wave inproportion to the variation in the pressure of said body of gas.

OSKAR STE'ITLER.

